1. Field Of The Invention
The present invention relates generally to antennas, and more particularly relates to a microstrip collinear antenna.
2. Description Of The Prior Art
Omnidirectional personal communication service (PCS) antennas are increasingly becoming important antennas in the cellular communication industry. Omnidirectional personal communication service (PCS) antennas are small, lightweight, easily affixed to buildings and other structures in and around cities and suburban communities, and more aesthetically pleasing when compared to the otherwise huge radio antenna towers that have been known in the cellular communication industry.
There are many known omnidirectional personal communication service (PCS) antennas in the prior art. In general, omnidirectional PCS antennas are constructed as sleeve dipoles or wire antennas with element spacings of 0.75 .lambda. in order to achieve proper radiation patterns. A traditional collinear design would require transposed coaxial 1/2 .lambda. element sections directly connected. In addition, these antennas have narrow patterns and impedance bandwidths.
In particular, U.S. Pat. No. 3,031,668 shows in FIGS. 1-2 and describes a dielectric loaded collinear vertical dipole antenna having a sequence of coaxial cable sections 12-18, a 1/4 .lambda. coaxial cable bottom section 11, a 1/4 .lambda. coaxial cable bottom section 21, radially disposed conductive spokes 19, an antenna feed cable 20, and a signal translating circuit 50.
An IRE Convention Record, Volume 4, Part 1 (1956), entitled "A Vertical Antenna Made of Transposed Sections of Coaxial Cable", by H. Wheeler, shows in FIGS. 1(a)-(b) and describes a vertical antenna having a series of solid dielectric coaxial cables with inner and outer conductors transposed at every junction. Each section has an effective length of 1/2 .lambda. in the solid dielectric coaxial cable, so the radiating gaps between the sections are all excited in the same polarity.
One known company in the industry has a PCS antenna described in a readily available specification. The Cushcraft PCS antenna appears to be a 6 dBd low profile omnidirectional antenna that operates in a frequency range of 1850-1990 Megahertz (Mhz), although the specification does not make clear the design thereof.
The prior art omnidirectional antennas suffer from a number of disadvantages, including having inconsistent pattern performance across their operating range as shown in FIGS. 16-18, requiring large element spacings and longer physical lengths, being difficult to assemble and labor intensive, and being very expensive and cost prohibitive.